Figure 9A. A dike of dark-colored rock cutting through granite. A dike is a thin sheet of igneous rock such as this, which forms below the earth's surface. Molten rock intruded along a fracture in the granite long after the granite had formed and cooled, but was still beneath the surface. This relationship indicates that the dike is younger than the granite. The dike rock is basalt, a very fine-grained, dark-colored rock. (Modern beach sand partly covers the bedrock.)

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Last updated on October 4, 2012

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